Providing curl to papermaking fibers is known in the art. There is disclosed for example in U.S. patent application Ser. No. 09/793,863 to Lee a process for producing high bulk cellulosic fibers exhibiting durable curl. The method of the '863 application involves curling the fiber in a disk refiner at elevated temperature and pressure. See Publication No. US 2001/0040015. Other references relating to fiber curling include U.S. Pat. No. 4,409,065 to Kasser; U.S. Pat. No. 4,431,479 to Barbe et al.; U.S. Pat. No. 4,976,819 to Minton; U.S. Pat. No. 5,501,768 to Hermans et al.; as well as U.S. Pat. No. 5,772,845 to Farrington et al.
Rotoclaves have been used to recycle waste paper. In this regard there is disclosed in U.S. Pat. No. 6,548,240 to Bouchette et al. a method of separating fiber from difficult to process coated and ink paper products. Further discussion of the rotoclave apparatus and its use for repulping may be found in U.S. Pat. No. 4,974,781 to Placzek and U.S. Pat. No. 5,119,994 also to Placzek.
It has been found that certain fibers may be provided with unexpectedly elevated and durable curl by treating them in fibrous form in pressure vessels at 35-90 psig in saturated steam with mechanical agitation. The fiber to be curled is maintained in an aqueous dispersion having an intermediate to relatively high consistency.